Vista - Microphone issue

Hi,

I am running the latest version of Messenger on Vista Business with a
Logitech Ultra-vision webcam with built in mic'. When I check my audio and
video settings everything is OK. However, when I establish a video chat
with someone then the picture is perfect both ways and I can hear the other
person but they cannot hear me. My mic' icon is grayed out with no movement
on sound levels. If both sides log onto Skype sound and vision work in both
directions. I prefer the Messenger interface and the picture quality is
better, so I would prefer to find a solution to this issue.

Any ideas?

thanks